In the drilling of offshore petroleum or gas producing wells from a fixed platform it is customary to insert a conductor member into the marine structure between the work deck and the well head. This conductor serves the primary purpose of enclosing the rotating drill string. Thus, drilling mud can be circulated through the drill string and returned to the deck.
In some instances where the petroleum bearing reservoir is determined to be relatively close to the surface of the water, it is necessary to offset the rotating drill string rather quickly so it will assume a desired direction whereby to enter the reservoir. In shallow areas this offsetting of the drill string from vertical must be accomplished as soon as possible so that the drill will intersect the reservoir within a short period of time.
It is known that by initially deflecting the drill string such that it enters the ocean floor at a desired angle, the operation is expedited. In one method of achieving such directional drilling a conductor is positioned within the offshore structure and aligned at an angle to the structure floor. Thus, the drill string by being guided through the conductor will enter the floor at a predetermined angle and direction.
It is also known that to effectuate the desired offset, the drill string can be initially forced from a vertical disposition into the desired angle. This is normally done through use of an elongated conductor guide which is carried within the body of the marine platform. The guide comprises a heavy walled tube-like member which is preformed into a desired curved configuration. Addition of curved or straight guide members to the marine structure after it has been placed at an offshore site is usually an expensive operation requiring the use of several divers.
The instant invention provides a novel arrangement in an offshore structure which serves the purposes of facilitating the drilling operation. It further serves to reduce the overall operating expenses and provides the structure with a greater degree of versatility due to the greater number of wells that can be drilled from a single position.
The marine structure is thus provided not only with ordinary drilling equipment such as derrick, rotary table and the like, but also with an elongated cage or substructure which serves to support a number of conductor guides. The cage can be detached from its normal submerged position in the marine structure and raised to the working deck or adjacent to the latter. Thereafter, the number of, or the pattern of conductor guides, can be changed by addition to or removal of said guides to achieve a desired drilling pattern at the ocean floor. Further, the cage can be realigned with respect to the structure prior to being reinserted into its seating or working position. Thus, the original conductor guides or the newly inserted guides can be disposed to permit further drilling in a particular direction from an initially upright disposition.
It is therefore an object to provide a marine structure capable of drilling wellbores into the ocean floor and exhibiting drilling versatility. A further object is to provide a marine drilling apparatus of the type contemplated which is particularly adept at drilling directionally away from a working site.